Liquid crystal display device

ABSTRACT

The liquid crystal display device of this invention includes a first substrate, a second substrate, and a vertical alignment type liquid crystal layer including liquid crystal molecules having negative dielectric anisotropy disposed between the two substrates. In each of a plurality of picture-element regions, the liquid crystal layer has a plurality of liquid crystal regions different in the direction in which liquid crystal molecules tilt upon application of a voltage. At least one of the first and second substrates has a light-shield layer overlapping at least part of boundary region defined as regions separating the plurality of liquid crystal regions from each other. The part of the boundary region overlapping the light-shield layer is a region permitting liquid crystal molecules surrounding the region to tilt so that the ends of the liquid crystal molecules closer to the substrate having the light-shield layer go away from the region upon application of a voltage.

BACKGROUND OF THE INVENTION

The present invention relates to a liquid crystal display device, andmore particularly, to a liquid crystal display device having a wideviewing angle characteristic and providing high quality display.

The liquid crystal display device is a flat display device havingexcellent features of being thin, light in weight and low in powerconsumption. However, the liquid crystal display device has ashortcoming of being large in “viewing angle dependence” in which thedisplay state changes with the direction in which the display device isobserved. A main cause for the large viewing angle dependence of theliquid crystal display device is that liquid crystal molecules havinguniaxial optical anisotropy are oriented uniformly in the display plane.

To improve the viewing angle characteristic of the liquid crystaldisplay device, an orientation division method is effective, in which aplurality of regions different in orientation states are formed in eachpicture-element region. Various techniques have been proposed toimplement this method. Among these, a technique disclosed in JapaneseLaid-Open Patent Publication No. 6-301036 and No. 2000-47217 and atechnique called MVA disclosed in Japanese Laid-Open Patent PublicationNo. 11-242225 are considered as typical techniques for implementing theorientation division on vertical alignment mode liquid crystal displaydevices.

In the technique disclosed in Japanese Laid-Open Patent Publication No.6-301036 and No. 2000-47217, an inclined electric field is generated byforming slits (openings) for an electrode, to control the orientationdirection of liquid crystal molecules with the generated inclinedelectric field.

In the MVA technique disclosed in Japanese Laid-Open Patent PublicationNo. 11-242225, a pair of substrates (for example, a TFT substrate and acolor filter substrate) opposed to each other via a liquid crystal layerhave protrusions, depressions or slits (openings of an electrode) formedon their surfaces facing the liquid crystal layer, to thereby realizethe orientation division.

As the type of the orientation division of each picture-element region,there are comparatively simple types, such as two-division type in whichliquid crystal molecules in each picture-element region are oriented intwo directions and four-division type in which they are oriented in fourdirections, and comparatively complicate types, such asinfinite-division type in which liquid crystal molecules are oriented inall directions and the type in which liquid crystal molecules aretwisted in a liquid crystal layer.

From the standpoint of achieving equal display characteristics in alldirections, liquid crystal molecules are preferably oriented in as manydirections as possible in each picture-element region. In general,orientation in four or more directions is considered providingsufficient display quality.

However, as a result of examinations by the present inventors, it wasfound that the techniques disclosed in Japanese Laid-Open PatentPublication No. 6-301036, No. 2000-47217 and No. 11-258606 had thefollowing problem. Although the azimuthal angle dependence of thedisplay characteristics can be improved by these techniques, the displaycharacteristics obtained when the display device is observed from thefront is greatly different from that obtained when it is observedobliquely. Therefore, the gray-scale characteristic greatly varies withthe angle at which the observer views the display plane, and this makesthe observer feel unnatural.

SUMMARY OF THE INVENTION

The present invention was devised to overcome the aforementioneddisadvantages, and an object of the present invention is providing aliquid crystal display device with high display quality that has a wideviewing angle characteristic and can provide display free fromunnaturalness.

The liquid crystal display device of the present invention includes afirst substrate, a second substrate, and a vertical alignment typeliquid crystal layer including liquid crystal molecules having negativedielectric anisotropy disposed between the first substrate and thesecond substrate, the device having a plurality of picture-elementregions each defined by a first electrode placed in the first substrateon the side facing the liquid crystal layer and a second electrodeplaced in the second substrate to oppose to the first electrode via theliquid crystal layer, in each of the plurality of picture-elementregions, the liquid crystal layer having a plurality of liquid crystalregions different in the direction in which liquid crystal moleculestilt when a voltage is applied between the first electrode and thesecond electrode, wherein at least one of the first substrate and thesecond substrate has a light-shield layer overlapping (lying above orbelow) at least part of boundary region defined as regions separatingthe plurality of liquid crystal regions from each other, and the atleast part of boundary region overlapping (lying above or below) thelight-shield layer is a region permitting liquid crystal moleculessurrounding the region to tilt so that ends of the liquid crystalmolecules closer to the substrate having the light-shield layer go awayfrom the region when a voltage is applied between the first electrodeand the second electrode.

Preferably, the light-shield layer is placed with a predeterminedspacing from the liquid crystal layer.

Alternatively, the liquid crystal display device of the presentinvention includes a first substrate, a second substrate, and a verticalalignment type liquid crystal layer including liquid crystal moleculeshaving negative dielectric anisotropy disposed between the firstsubstrate and the second substrate, the device having a plurality ofpicture-element regions each defined by a first electrode placed in thefirst substrate on the side facing the liquid crystal layer and a secondelectrode placed in the second substrate to oppose to the firstelectrode via the liquid crystal layer, in each of the plurality ofpicture-element regions, the liquid crystal layer having a plurality ofliquid crystal regions different in the direction in which liquidcrystal molecules tilt when a voltage is applied between the firstelectrode and the second electrode, the plurality of liquid crystalregions of the liquid crystal layer including a first liquid crystalregion of which the retardation value for light incident on the liquidcrystal layer obliquely from the normal to the liquid crystal layerincreases with rise of an applied voltage and a second liquid crystalregion of which the retardation value first decreases and thenincreases, wherein the device includes a light-shield layer selectivelyshading the first liquid crystal region when the device is observed in adirection oblique from the normal to the display plane.

The liquid crystal display device described above may further include apair of polarizing plates placed opposing to each other via the liquidcrystal layer so that their polarization axes are substantiallyperpendicular to each other, wherein in each of the plurality ofpicture-element regions, at least one of the first substrate and thesecond substrate may have an additional light-shield layer overlapping(lying above or below) at least part of regions in which liquid crystalmolecules tilt in directions substantially parallel to the polarizationaxes of the pair of polarizing plates when a voltage is applied betweenthe first electrode and the second electrode.

Alternatively, the liquid crystal display device of the presentinvention includes a first substrate, a second substrate, a verticalalignment type liquid crystal layer including liquid crystal moleculeshaving negative dielectric anisotropy disposed between the firstsubstrate and the second substrate, and a pair of polarizing platesplaced opposing to each other via the liquid crystal layer so that theirpolarization axes are substantially perpendicular to each other, thedevice having a plurality of picture-element regions each defined by afirst electrode placed in the first substrate on the side facing theliquid crystal layer and a second electrode placed in the secondsubstrate to oppose to the first electrode via the liquid crystal layer,in each of the plurality of picture-element regions, the liquid crystallayer having a plurality of liquid crystal regions different in thedirection in which the liquid crystal molecules tilt when a voltage isapplied between the first electrode and the second electrode, wherein ineach of the plurality of picture-element regions, at least one of thefirst substrate and the second substrate has a light-shield layeroverlapping (lying above or below) at least part of regions in whichliquid crystal molecules tilt in directions substantially parallel tothe polarization axes of the pair of polarizing plates when a voltage isapplied between the first electrode and the second electrode.

Preferably, the light-shield layer is placed substantially right on theliquid crystal layer.

At least one of the first substrate and the second substrate may have atleast one protrusion having a slant side formed on the surface facingthe liquid crystal layer, and the direction in which liquid crystalmolecules tilt in each of the plurality of liquid crystal regions may bedefined by orientation-regulating force of the at least one protrusion.

Otherwise, at least one of the first electrode and the second electrodemay have at least one opening, and the direction in which liquid crystalmolecules tilt in each of the plurality of liquid crystal regions may bedefined by an inclined electric field generated at an edge portion ofthe at least one opening when a voltage is applied between the firstelectrode and the second electrode.

Otherwise, at least one of the first substrate and the second substratemay have at least one protrusion having a slant side formed on thesurface facing the liquid crystal layer, at least one of the firstelectrode and the second electrode may have at least one opening, andthe direction in which liquid crystal molecules tilt in each of theplurality of liquid crystal regions may be defined byorientation-regulating force of the at least one protrusion and aninclined electric field generated at an edge portion of the at least oneopening when a voltage is applied between the first electrode and thesecond electrode.

In a preferred embodiment, the first substrate further includesswitching elements respectively placed to correspond to the plurality ofpicture-element regions, and the first electrode includes a plurality ofpicture-element electrodes respectively placed for the plurality ofpicture-element regions and switched with the switching elements, andthe second electrode includes at least one counter electrode opposed tothe plurality of picture-element electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B diagrammatically show a liquid crystal display device100 of Embodiment 1 of the present invention, where FIG. 1A is a topview and FIG. 1B is a cross-sectional view taken along line 1B-1B′ inFIG. 1A.

FIGS. 2A and 2B diagrammatically show a conventional liquid crystaldisplay device 1000 having no light-shield layer, where FIG. 2A is a topview and FIG. 2B is a cross-sectional view taken along line 2B-2B′ inFIG. 2A.

FIG. 3 is a graph showing the voltage-transmittance characteristicsobtained when the liquid crystal display device 1000 is observed in anormal direction D1 and in an oblique direction D2.

FIG. 4 is a graph showing the voltage-transmittance characteristicsobtained when a liquid crystal region 31 in which liquid crystalmolecules 30 a tilt to fall toward the observer is observed in anoblique direction and when a liquid crystal region 31 in which liquidcrystal molecules 30 a tilt to fall toward the opposite to the observeris observed in an oblique direction.

FIG. 5 is a graph showing the voltage-transmittance characteristicsobtained when the liquid crystal display device 100 of Embodiment 1 isobserved in the normal direction D1 and in the oblique direction D2.

FIG. 6 is a diagrammatic cross-sectional view of the liquid crystaldisplay device 100 of Embodiment 1.

FIGS. 7A and 7B diagrammatically show another liquid crystal displaydevice 100A of Embodiment 1 of the present invention, where FIG. 7A is atop view and FIG. 7B is a cross-sectional view taken along line 7B-7B′in FIG. 7A.

FIGS. 8A and 8B diagrammatically show yet another liquid crystal displaydevice 100B of Embodiment 1 of the present invention, where FIG. 8A is atop view and FIG. 8B is a cross-sectional view taken along line 8B-8B′in FIG. 8A.

FIGS. 9A and 9B diagrammatically show a liquid crystal display device200 of Embodiment 2 of the present invention, where FIG. 9A is a topview and FIG. 9B is a cross-sectional view taken along line 9B-9B′ inFIG. 9A.

FIGS. 10A and 10B diagrammatically show another liquid crystal displaydevice 200A of Embodiment 2 of the present invention, where FIG. 10A isa top view and FIG. 10B is a cross-sectional view taken along line10B-10B′ in FIG. 10A.

FIGS. 11A and 11B diagrammatically show yet another liquid crystaldisplay device 200B of Embodiment 2 of the present invention, where FIG.11A is a top view and FIG. 11B is a cross-sectional view taken alongline 11B-11B′ in FIG. 11A.

FIGS. 12A and 12B diagrammatically show a liquid crystal display device300 of Embodiment 3 of the present invention, where FIG. 12A is a topview and FIG. 12B is a cross-sectional view taken along line 12B-12B′ inFIG. 12A.

FIG. 13 is a diagrammatic top view of the liquid crystal display device300 of Embodiment 3.

FIG. 14 is a graph showing the voltage-transmittance characteristic of aregion in which liquid crystal molecules 30 a tilt along a polarizationaxis PA1 obtained when the liquid crystal display device 1000 isobserved in an oblique direction along a polarization axis PA2.

FIG. 15 is a graph showing the voltage-transmittance characteristicsobtained when the liquid crystal display device 300 of Embodiment 3 isobserved in the normal direction and in an oblique direction.

FIG. 16 is a graph showing the voltage-transmittance characteristicsobtained when the liquid crystal display device 100 is observed in thenormal direction and in an oblique direction, and thevoltage-transmittance characteristic obtained when a liquid crystaldisplay device having an additional light-shield layer is observed in anoblique direction.

FIG. 17 is a diagrammatic top view of a liquid crystal display device400 of Embodiment 4 of the present invention.

FIG. 18 is a diagrammatic top view of another liquid crystal displaydevice 400A of Embodiment 4 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the pre-sent invention will bedescribed with reference to the accompanying drawings. Since excellentdisplay characteristics can be obtained according to the presentinvention, the present invention is suitably applied to active matrixliquid crystal display devices. Herein, as embodiments of the presentinvention, active matrix liquid crystal display devices having thin filmtransistors (TFTs) as the switching elements for switchingpicture-element electrodes will be described. The present invention canalso be applied to MIM type active matrix liquid crystal display devicesand simple active matrix liquid crystal display devices.

As used herein, a region of a liquid crystal display devicecorresponding to one “picture element” as the minimum unit of display iscalled a “picture-element region”. In a color liquid crystal displaydevice, R, G and B “picture elements” constitute one “pixel”. In anactive matrix liquid crystal display device, a picture-element electrodeand a portion of a counter electrode opposed to the picture-elementelectrode define a picture-element region. In a simple matrix liquidcrystal display device, each of the crossings of stripe-shaped columnelectrodes and stripe-shaped row electrodes running perpendicular toeach other defines a picture-element region. If a black matrix isplaced, the picture-element region is strictly defined as a portion of aregion across which a voltage is applied according to the state to bedisplayed that corresponds to each opening of the black matrix.

Embodiment 1

The structure of a liquid crystal display device 100 of Embodiment 1 ofthe present invention will be described with reference to FIGS. 1A and1B. Note that in the following description, color filters and a blackmatrix are ignored for simplification. Throughout the drawings,components having the same functions are denoted by the same referencenumerals and are not described repeatedly. FIG. 1A is a top view of theliquid crystal display device 100 as viewed in the direction normal tothe substrate plane, and FIG. 1B is a cross-sectional view taken alongline 1B-1B′ in FIG. 1A. FIGS. 1A and 1B show the state under applicationof a voltage across the liquid crystal layer.

The liquid crystal display device 100 includes an active matrixsubstrate (hereinafter, called a “TFT substrate”) 10 a, a countersubstrate (also called a “color filter substrate”) 10 b, and a verticalalignment type liquid crystal layer 30 disposed between the TFTsubstrate 10 a and the counter substrate 100 b.

Liquid crystal molecules 30 a in the liquid crystal layer 30, which havenegative dielectric anisotropy, are aligned vertically to the surfacesof vertical alignment films (not shown) formed on the surfaces of theTFT substrate 100 a and the counter substrate 100 b facing the liquidcrystal layer 30 when no voltage is applied across the liquid crystallayer 30. That is, the liquid crystal layer 30 is in a verticallyaligned state during non-voltage application. Note however that theliquid crystal molecules 30 a in the liquid crystal layer 30 in thevertically aligned state may somewhat be tilted from the normal to thesurfaces of the vertical alignment films (surfaces of the substrates)depending on the kind of the vertical alignment films and the kind ofthe liquid crystal material. In general, when the axes (also called the“axial directions”) of liquid crystal molecules are at about 85° or morewith respect to the surfaces of the vertical alignment films, this stateis called the vertically aligned state.

The TFT substrate 10 a of the liquid crystal display device 100 includesa transparent plate (glass plate, for example) 11 and picture-elementelectrodes 14 formed on the surface of the transparent plate 11. Thecounter substrate 100 b includes a transparent plate (glass plate, forexample) 21 and a counter electrode 24 formed on the surface of thetransparent plate 21. The orientation state of the liquid crystal layer30 in each picture-element region changes with the voltage appliedbetween the corresponding picture-element electrode 14 and the counterelectrode 24 opposed to each other via the liquid crystal layer 30. Asthe orientation state of the liquid crystal layer 30 changes, thepolarized state and amount of light passing through the liquid crystallayer 30 change, and using this phenomenon, display is achieved. In thisembodiment, a pair of polarizing plates (not shown) are opposed to eachother via the TFT substrate 10 a and the counter substrate 100 b so thattheir polarization axes (transmission axes) PA1 and PA2 are orthogonalto each other.

In the liquid crystal display device 100, each picture-element region isdivided in terms of the orientation to improve the viewing anglecharacteristic, in which the liquid crystal layer 30 includes aplurality of liquid crystal regions 31 different in the direction inwhich the liquid crystal molecules 30 a tilt (the orientation of themajor axes of the tilting liquid crystal molecules 30 a orthogonallyprojected on the substrate surface: azimuthal direction). Arrows 36 inFIG. 1A indicate the directions in which the liquid crystal molecules 30a in the liquid crystal regions 31 tilt, and in this case, indicate thedirections in which the ends of the liquid crystal molecules 30 a closerto the counter substrate 100 b fall upon application of a voltage.

The direction in which the liquid crystal molecules 30 a tilt is definedby an orientation-regulating structure placed on the side of the TFTsubstrate 100 a and an orientation-regulating structure placed on theside of the counter substrate 10 b. Hereinafter, this will be describedin detail.

The picture-element electrode 14 of the TFT substrate 10 a has aplurality of openings 14 a. In this embodiment, the openings 14 a,having a shape of a slit (a shape having a width (side orthogonal to thelength) extremely small with respect to the length), extend in parallelwith each other. Each opening 14 a has a side extending at an angle of45° with respect to the longitudinal and lateral sides of thepicture-element electrode 14. The direction in which the side of theopening 14 a extends changes by 90° every predetermined pitch, forming azigzag (or dogleg) shape. In this embodiment, the openings 14 a of thepicture-element electrode 14 are formed to have a width of 10 μm and apitch of 60 μm.

When a voltage is applied between the picture-element electrode 14 andthe counter electrode 24, an inclined electric field represented by aninclined equipotential line is formed in a region of the liquid crystallayer 30 located above an edge portion of each opening 14 a of thepicture-element electrode 14 (a portion around the inside of eachopening 14 a including the boundary (fringe) of the opening 14 a).Therefore, when a voltage is applied, the liquid crystal molecules 30 ahaving negative dielectric anisotropy, which are in the verticallyaligned state during non-voltage application, tilt along the inclinationof the inclined electric field generated in the edge portion of theopening 14 a.

The counter substrate 100 b has protrusions 26 on the surface thereoffacing the liquid crystal layer 30. Each protrusion 26 has slant sides26 s and extends in a zigzag (or dogleg) shape as viewed in thedirection normal to the substrate surface, as in the case of theopenings 14 a. The direction in which the slant sides 26 s extendcorresponds with the direction in which the sides of the openings 14 aextend, and the protrusion 26 is placed roughly in the middle betweenthe two adjacent openings 14. In this embodiment, the protrusions 16 areformed to have a width of 10 μm and a pitch of 60 μm.

The surface of the protrusion 26 has a vertical alignment property(typically, a vertical alignment film (not shown) is formed to cover theprotrusion 26). Therefore, liquid crystal molecules 30 a on the slantsides 26 s are aligned substantially vertically to the slant sides 26 sdue to the anchoring effect of the slant sides 26 s.

When a voltage is applied across the liquid crystal layer 30 in thestate described above, other liquid crystal molecules 30 a in thevicinity of the protrusion 26 tilt to conform to the inclinedorientation on the slant sides 26 s of the protrusion 26 caused due tothe anchoring effect of the slant sides 26 s.

As described above, the direction of the tilt of the liquid crystalmolecules 30 a located above the edge portion of the opening 14 a of thepicture-element electrode 14 upon application of a voltage is defined bythe orientation-regulating structure of the TFT substrate 100 a, thatis, the picture-element electrode 14 having the opening 14 a. Also, thedirection of the tilt of the liquid crystal molecules 30 a located inthe vicinity of the protrusion 26 upon application of a voltage isdefined by the orientation-regulating structure of the counter substrate10 b, that is, the protrusion 26 having the slant sides 26 s. Therefore,upon application of a voltage, the remaining liquid crystal molecules 30a tilt to conform to the tilt of these liquid crystal molecules 30 alocated in the portions described above. As a result, the direction ofthe tilt of the liquid crystal molecules 30 a in each liquid crystalregion 31 is defined by the inclined electric field generated in theedge portion of the opening 14 a of the picture-element electrode 14 andthe orientation-regulating force of the protrusion 26 on the countersubstrate 100 b.

As shown in FIG. 1A, the picture-element region of the liquid crystaldisplay device 100 includes a plurality of liquid crystal regions 31different in the direction of the tilt of the liquid crystal molecules30 a. In the illustrated example, the picture-element region is dividedto provide four directions apart by angles of integral multiples of 90°from one another, and these four directions are at an angle of about 45°with respect to the polarization axes PA1 and PA2 of polarizing plates.

In the liquid crystal display device 100 according to the presentinvention, the TFT substrate 10 a further includes light-shield layers40. As shown in FIG. 1B, each light-shield layer 40 is formed to overlap(lie below) at least part of boundary region 33 defined as regionseparating the plurality of liquid crystal regions 31 from one another.

More specifically, in this embodiment, the light-shield layer 40 has thesame width of 10 μm as the protrusion 26, so as to be the same in shapeas viewed in the direction normal to the substrate as the protrusion 26and extend below the protrusion 26. Note that in FIG. 1B, the width ofthe light-shield layer 40 is exaggerated for the purpose of easyunderstanding of description to follow. In the illustrated example, atransparent insulating layer 12 is formed covering the light-shieldlayer 40 formed on the transparent plate 11, so that a predeterminedspacing is provided between the light-shield layer 40 and the liquidcrystal layer 30.

As shown in FIG. 1B, the boundary region 33 overlapping (lying above)the light-shield layer 40 corresponds to a region permitting liquidcrystal molecules 30 a surrounding the region to tilt so that ends 30 a1 of the liquid crystal molecules 30 a closer to the TFT substrate 100a, that is, the substrate having the light-shield layer 40 go away fromthis region when a voltage is applied between the picture-elementelectrode 14 and the counter electrode 24.

The liquid crystal display device 100, having the light-shield layers 40placed as described above, is small in the difference of the displaycharacteristics between observation from the front and observation in anoblique direction, and thus can provide display free from unnaturalness.This will be described in detail as follows.

First, referring to FIGS. 2A and 2B, why a conventional liquid crystaldisplay device 1000 having no light-shield layer makes the viewer feelunnatural will be described.

The conventional liquid crystal display device 1000 of FIGS. 2A and 2Bhas substantially the same structure as the liquid crystal displaydevice 100 except that the former has no light-shield layer overlappingat least part of the boundary region 33.

In the liquid crystal display device 1000, the azimuthal angledependence of the display characteristics is improved because eachpicture-element region is divided into a plurality of liquid crystalregions 31. However, a great difference arises in displaycharacteristics between observation from the front and observation in anoblique direction.

FIG. 3 is a graph showing the normalized voltage-transmittancecharacteristic obtained when the liquid crystal display device 1000 isobserved in the normal direction (direction indicated by arrow D1 inFIG. 2B) and the normalized voltage-transmittance characteristicobtained when it is observed in an oblique direction (directionindicated by arrow D2 in FIG. 2B) at a visual angle tilted along thepolarization axis PA1. In FIG. 3, the axis of abscissas represents theapplied voltage (V) across the liquid crystal layer 30 and the axis ofordinates represents the normalized transmittance.

As shown in FIG. 3, a voltage-transmittance curve L2 obtained duringobservation in an oblique direction is sharper than avoltage-transmittance curve L1 obtained during observation in the normaldirection. In the state of application of a gray-scale voltage, thetransmittance obtained during observation in an oblique direction(normalized transmittance) is higher than the transmittance obtainedduring observation in the normal direction.

The increase of the transmittance in an oblique direction duringapplication of a gray-scale voltage is caused by the behavior of liquidcrystal molecules 30 a in a specific liquid crystal region 31 among theplurality of liquid crystal regions 31 of each picture-element region.Specifically, it is caused by the behavior of the liquid crystalmolecules 30 a tilting in the direction opposite to the observer whoobserves obliquely (that is, tilting so that the ends of the liquidcrystal molecules 30 a closer to the counter substrate 100 b go awayfrom the observer).

The above discussion will be made in more detail focusing on the twoliquid crystal regions 31 shown in FIG. 2B. The liquid crystal molecules30 a in both liquid crystal regions 31 tilt at an angle of 45° withrespect to the polarization axes PA1 and PA2 as shown in FIG. 2A.However, when the two liquid crystal regions 31 are observed in anoblique direction (direction indicated by arrow D2 in FIG. 2B) at avisual angle tilted along the polarization axis PA1, for example, theliquid crystal molecules 30 a in the liquid crystal region 31 on theleft as viewed from FIG. 2B tilt to fall toward the observer, whilethose in the liquid crystal region 31 on the right tilt to fall towardthe opposite to the observer.

FIG. 4 is a graph showing the voltage-transmittance characteristicobtained when the two liquid crystal regions 31 shown in FIG. 2B areobserved in an oblique direction, in which a voltage-transmittance curveL3 is for the liquid crystal region 31 in which the liquid crystalmolecules 30 a tilt to fall toward the observer (liquid crystal regionon the left in FIG. 2B), and a voltage-transmittance curve L4 is for theliquid crystal region 31 in which the liquid crystal molecules 30 a tiltto fall toward the opposite to the observer (liquid crystal region onthe right in FIG. 2B).

As shown in FIG. 4, in the liquid crystal region 31 in which the liquidcrystal molecules 30 a fall toward the observer, the transmittance firstdrops and then rises with rise of the voltage. In the liquid crystalregion 31 in which the liquid crystal molecules 30 a fall toward theopposite to the observer, the transmittance rises roughly monotonouslywith rise of the voltage. The reason is that, while the retardationvalue of the liquid crystal layer 30 for light incident obliquely to theliquid crystal layer 30 (in a direction oblique from the normal to theliquid crystal layer 30) first decreases and then increases with rise ofthe voltage in the liquid crystal region 31 in which the liquid crystalmolecules 30 a fall toward the observer, it increases monotonously withrise of the voltage in the liquid crystal region 31 in which the liquidcrystal molecules 30 a fall toward the opposite to the observer.

The voltage-transmittance characteristic obtained during observation inan oblique direction shown in FIG. 3 represents the sum of thevoltage-transmittance characteristics of the respective liquid crystalregions 31 as those shown in FIG. 4. It is therefore considered that theincrease of the transmittance in an oblique direction during applicationof a gray-scale voltage is caused by the liquid crystal molecules 30 afalling toward the opposite to the observer.

In the liquid crystal display device 100 according to the presentinvention, the light-shield layer 40 is formed to overlap (lie below) atleast part of the boundary region 33 defined as region separating theplurality of liquid crystal regions 31 from one another. The at leastpart of the boundary region 33 that is overlapping (lying above) thelight-shield layer 40 is a region permitting the liquid crystalmolecules 30 a surrounding the region to tilt so that the ends of theliquid crystal molecules 30 a closer to the TFT substrate 10 a, that is,the substrate having the light-shield layer 40 go away from this regionwhen a voltage is applied.

The thus-provided light-shield layer 40 selectively shades the liquidcrystal region 31 in which the liquid crystal molecules 30 a tilt towardthe opposite to the observer, that is, the liquid crystal region 31 ofwhich the retardation value for light incident obliquely increasesroughly monotonously with rise of the voltage, among the two lightcrystal regions 31 adjacent to each other via the boundary region 33.

In FIG. 1B, W1 denotes the width of a region shaded by the light-shieldlayer 40 during observation in the normal direction D1, and W2 denotesthe width of a region shaded by the light-shield layer 40 duringobservation in the oblique direction D2. As shown in FIG. 1B, duringobservation in the normal direction, the light-shield layer 40 shadesthe region of the liquid crystal layer 30 right above the light-shieldlayer 40, and thus will not change the proportion of contribution to thefront-view display between the two liquid crystal regions 31. However,during observation in an oblique direction, in which parallax occurs,the light-shield layer 40 selectively shades the liquid crystal region31 in which the liquid crystal molecules 30 a fall toward the oppositeto the observer. FIG. 1B also shows the width W3 of a region shaded bythe light-shield layer 40 during observation in an oblique direction D3opposite to the oblique direction D2. As is found from FIG. 1B, duringobservation in the oblique direction D3, also, the light-shield layer 40selectively shades the liquid crystal region 31 in which the liquidcrystal molecules 30 a fall toward the opposite to the observer.

Therefore, the liquid crystal region 31 in which the liquid crystalmolecules 30 a fall toward the opposite to the observer partly fails tocontribute to the display observed in an oblique direction. Thissuppresses the increase of the transmittance in the oblique directionduring application of a gray-scale voltage, and thus brings thevoltage-transmittance characteristic during observation in the obliquedirection close to the voltage-transmittance characteristic duringobservation in the normal direction. As a result, the oblique-directiondisplay characteristics and the normal-direction display characteristicscan be made close to each other, and hence display free fromunnaturalness can be realized.

FIG. 5 shows a voltage-transmittance curve L3 obtained when the liquidcrystal display device 100 of this embodiment is observed in the normaldirection D1 and voltage-transmittance curves L4 and L5 obtained when itis observed in the oblique direction D2. The voltage-transmittancecurves L4 and L5 show the cases when the depth of the light-shield layer40, which is defined as the spacing between the bottom surface of thelight-shield layer 40 (surface farther from the liquid crystal layer 30)and the liquid crystal layer 30, is 3 μm and 5 μm, respectively. Thethickness of the liquid crystal layer 30 is 4 μm. FIG. 5 also shows thevoltage-transmittance curve L2 obtained when the conventional liquidcrystal display device 1000 is observed in the oblique direction D2 forcomparison.

As shown in FIG. 5, the voltage-transmittance curves L4 and L5 of theliquid crystal display device 100 obtained during observation in anoblique direction are closer in shape to the voltage-transmittance curveL3 obtained during observation in the normal direction than thevoltage-transmittance curve L2 of the display device having nolight-shield layer is. Therefore, natural display in which thenormal-direction display characteristics and the oblique-directiondisplay characteristics are close to each other is obtained.

The depth, width, shape and the like of the light-shield layer 40 arenot limited to those described in this embodiment, but may beappropriately set depending on the specifications of the liquid crystaldisplay device and desired transmittance, display characteristics andthe like.

The depth of the light-shield layer 40 may be set depending on thethickness of the liquid crystal layer 30, the size of the liquid crystalregions 31 and the like so that the liquid crystal region 31 can beeffectively shaded. To effectively shade a specific liquid crystalregion 31 by use of occurrence of parallax, the light-shield layer 40should preferably be placed with a predetermined spacing from the liquidcrystal layer 30, and the spacing between the light-shield layer 40 andthe liquid crystal layer 30, that is, the depth of the light-shieldlayer 40 should preferably be large to some extent. The parallax islarger when the light-shield layer 40 is placed with a predeterminedspacing from the liquid crystal layer 30 than when it is placedimmediately under the liquid crystal layer 30. In the former case, theliquid crystal region 31 can be sufficiently shaded even if the visualangle (the tilt angle from the normal to the display plane) iscomparatively small. As is found from FIG. 5, in this embodiment, theoblique-direction voltage-transmittance characteristic can be broughtcloser to the normal-direction voltage-transmittance characteristic whenthe depth of the light-shield layer 40 is 5 μm than when it is 3 μm.

A preferred depth of the light-shield layer 40 will be described withreference to FIG. 6. In this embodiment, the liquid crystal region 31can be effectively shaded by setting the depth D of the light-shieldlayer 40 to satisfy the relationship, D+T₃/2=√{square root over ()}3×P/2 where D is the depth of the light-shield layer (=thickness T₁ ofthe light-shield layer 40+thickness T₂ of the transparent insulatinglayer 12 existing on the light-shield layer 40, in this case), T₃ is thethickness of the liquid crystal layer 30, and P is the pitch ofarrangement of the protrusions 26 and the openings 14 a. By setting thedepth D of the light-shield layer 40 in this way, the center of thelight-shield layer 40 will shade roughly the middle of the regionbetween the protrusion 26 and the opening 14 a adjacent to each other,that is, the center portion of the liquid crystal region 31, when theliquid crystal display device is observed at a visual angle of 60°(assuming that the average refractive index of the components of theliquid crystal display device is 1.6 and the observation is made in theair having the refractive index of 1.0).

In this embodiment, the width W of the light-shield layer 40 was madesubstantially equal to the width of the protrusion 26. The width of thelight-shield layer 40 is not limited to this, but is preferably widerfrom the standpoint of further improving the display characteristics byshading a larger portion of the liquid crystal region 31 in which theliquid crystal molecules 30 a fall toward the opposite to the observer.In this case, the light-shield layer 40 may overlap part of the liquidcrystal region 31, not only the boundary region 33. A wider light-shieldlayer 40 may however decrease the transmittance during observation fromthe front. Therefore, from the standpoint of suppressing decrease of thetransmittance in the normal direction, the narrow light-shield layer 40is preferred. A side face of the light-shield layer 40 also functions toshade the liquid crystal region 31 due to occurrence of parallax.Therefore, the light-shield layer 40 may be: made thick to increase theregion of the side face and thereby enable shading of a larger portionof the liquid crystal region 31. Thus, even when the width of thelight-shield layer 40 is set comparative small, the liquid crystalregion 31 can be sufficiently shaded while preventing decrease of thetransmittance in the normal direction by increasing the thickness of thelight-shield layer 40.

The shape of the light-shield layer 40 is not limited to that describedabove. In the case that the light-shield layer 40 is opposed to theprotrusion 26 as in this embodiment (or opposed to the opening 14 a ofthe picture-element electrode as will be described later), loss intransmittance in the normal direction can be minimized by providing thelight-shield layer 40 of the same shape as the protrusion 26 (or opening14 a). The reason is that the liquid crystal molecules 30 a in theboundary region 31 facing the protrusion 26 (or opening 14 a) arealigned roughly vertically even during application of a voltage, tomaintain the conformity of the alignment with the surrounding liquidcrystal molecules 30 a. Therefore, the region of the liquid crystallayer 30 facing the protrusion 26 (or opening 14 a) is inherently low inthe proportion of contribution to the transmittance.

The light-shield layer 40 was placed only on the side of the TFTsubstrate 100 a in the above description. Alternatively, a light-shieldlayer 40 may be placed additionally or only on the side of the countersubstrate 100 b.

FIGS. 7A and 7B show another liquid crystal display device 100A of thisembodiment, which includes light-shield layers 40′ placed on the side ofthe counter substrate 100 b in addition to the light-shield layers 40placed on the side of the TFT substrate 100 a.

Each light-shield layer 40′ of the counter substrate 100 b is formed tooverlap (lie above) at least part of the boundary region 33. As shown inFIG. 7B, the at least part of the boundary region 33 that overlaps (liesbelow) the light-shield layer 40′ is a region permitting liquid crystalmolecules 30 a surrounding the region to tilt so that ends 30 a 2 of theliquid crystal molecules 30 a closer to the counter substrate 100 b,that is, the substrate having the light-shield layer 40′ go away fromthis region when a voltage is applied. A transparent insulating film 22is formed covering the light-shield layers 40′ formed on the transparentplate 21, and thus the light-shield layers 40′ are placed with apredetermined spacing from the liquid crystal layer 30.

Each light-shield layer 40′ of the counter substrate 100 b selectivelyshades the liquid crystal region 31 in which the liquid crystalmolecules 30 a fall toward the opposite to the observer, that is, theliquid crystal region 31 of which the retardation value for lightincident obliquely increases monotonously with rise of the voltage,among the liquid crystal regions 31 adjacent to each other via theboundary region 33.

In FIG. 7B, W4 denotes the width of a region shaded by the light-shieldlayer 40′ during observation in the normal direction D4, and W5 denotesthe width of a region shaded by the light-shield layer 40′ duringobservation in an oblique direction D5. As shown in FIG. 7B, duringobservation in the normal direction, the light-shield layer 40′ shadesthe region of the liquid crystal layer 30 right under the light-shieldlayer 40′. However, during observation in an oblique direction, thelight-shield layer 40′ selectively shades the liquid crystal region 31in which the liquid crystal molecules 30 a tilt toward the opposite tothe observer due to occurrence of parallax.

Thus, in the liquid crystal display device 10A, not only thelight-shield layers 40 on the side of the TFT substrate 100 a but alsothe light-shield layers 40′ on the side of the counter substrate 100 bselectively shade the liquid crystal regions 31 in which the liquidcrystal molecules 30 a tilt toward the opposite to the observer.Accordingly, the oblique-direction display characteristics can be madeclose to the normal-direction display characteristics, and thus displayfree from unnaturalness can be realized.

In the liquid crystal display device 100A shown in FIGS. 7A and 7B, thewidth of the light-shield layers 40 and 40′ is preferably equal to orlarger than the width of the protrusions 26 and the openings 14 a, andis preferably smaller than the pitch of arrangement of the protrusions26 and the openings 14 a (P in FIG. 6). If the width of the light-shieldlayers 40 and 40′ is equal to or larger than the pitch of arrangement ofthe protrusions 26 and the openings 14 a, the transmittance in thenormal direction will be almost zero.

As described above, in the liquid crystal display devices 100 and 10A,the light-shield layers 40 (40′) are placed on the side of the TFTsubstrate 10 a and/or on the side of the counter substrate 100 b, toenable selective shading of the liquid crystal regions 31 in which theliquid crystal molecules 30 a tilt toward the opposite to the observer.

On the side of which substrate the light-shield layer should be placedfor a certain boundary region 33 may be determined in the followingmanner. The liquid crystal molecules 30 a surrounding a boundary region33 tilt so that the ends of the liquid crystal molecules 30 a closer toeither one of the substrates go away from the boundary region 33. On theside of this substrate, the light-shield layer for the boundary region33 is placed. In other words, the light-shield layer should be placed sothat the liquid crystal molecules 30 a surrounding the regionoverlapping (lying above or below) the light-shield layer tilt so thatthe ends thereof closer to the substrate having the light-shield layergo away from the region upon application of a voltage.

Specifically, when the surrounding liquid crystal molecules 30 a tilt sothat the ends thereof closer to the TFT substrate 100 a go away from theboundary region (for example, when the light-shield layer is placed tocorrespond to the boundary region 33 facing the protrusion 26 shown inFIGS. 1B and 7B), the light-shield layer may be placed on the side ofthe TFT substrate 100 a. Likewise, when the surrounding liquid crystalmolecules 30 a tilt so that the ends thereof closer to the countersubstrate 100 b go away from the boundary region (for example, when thelight-shield layer is placed to correspond to the boundary region 33facing the opening 14 a shown in FIGS. 1B and 7B), the light-shieldlayer may be placed in the counter substrate 100 b.

In the liquid crystal display device according to the present invention,the light-shield layer is selectively placed on the side of either oneof the substrates determined by paying attention to the behavior of theliquid crystal molecules 30 a surrounding each boundary region 33 duringapplication of a voltage. Therefore, the liquid crystal regions 31 inwhich the liquid crystal molecules 30 a tilt toward the opposite to theobserver are selectively shaded in whichever oblique direction theobserver views the liquid crystal display device, and thus naturaldisplay free from unnaturalness can be realized. Since the boundaryregions shaded by the light-shield layers during observation in thenormal direction are typically regions that hardly contribute to thedisplay inherently (even without the light-shield layers), it isunlikely to decrease the transmittance due to the placement of thelight-shield layers.

The light-shield layers are made of a light-shield material such asmetal including aluminum and resin, and may be formed at an arbitrarystage in the process of fabrication of the TFT substrate 10 a and thecounter substrate 100 b so that a predetermined spacing is providedbetween the light-shield layers and the liquid crystal layer 30. If thelight-shield layers are formed of a film commonly used for scanninglines and signal lines formed on the transparent plate 11 of the TFTsubstrate 100 a, no new step is required for formation of thelight-shield layers. The light-shield layers may shade substantially theentire incident light incident thereon, or may be a translucent filmallowing passing of part of incident light.

In this embodiment, the TFT substrate 10 a includes the picture-elementelectrodes 14 having the openings (slits) 14 a as theorientation-regulating structure, and the counter substrate 100 bincludes the protrusions 26 having the slant sides 26 s as theorientation-regulating structure. The present invention is not limitedto this, but may be suitably applied to other liquid crystal displaydevices having a structure permitting orientation division of thepicture-element regions. For example, a liquid crystal display device100B shown in FIGS. 8A and 8B may be adopted, in which the TFT substrate100 a has protrusions 16 having slant sides 16 s and the countersubstrate 100 b has a counter electrode 24 having openings 24 a. Onlyone substrate may have an orientation-regulating structure (for example,electrodes having openings and protrusions). However, from thestandpoint of stability of alignment, both substrates preferably haverespective orientation-regulating structures.

Embodiment 2

FIGS. 9A and 9B show a liquid crystal display device 200 of Embodiment 2according to the present invention, where FIG. 9A is a top view of theliquid crystal display device 200 as viewed in the direction normal tothe substrate, and FIG. 9B is a cross-sectional view taken along line9B-9B′ in FIG. 9A. FIGS. 9A and 9B show the state under application of avoltage across the liquid crystal layer.

In the liquid crystal display device 100 of Embodiment 1, eachpicture-element region was divided into four in terms of the orientationso that the liquid crystal molecules are oriented in four directions. Inthe liquid crystal display device 200 of Embodiment 2, eachpicture-element region is divided into an infinite number in terms ofthe orientation so that the liquid crystal molecules are oriented in alldirections.

A TFT substrate 200 a of the liquid crystal display device 200 includespicture-element electrodes 14 having openings 14 a as anorientation-regulating structure. The openings 14 a are slits formed ina square grid pattern.

A counter substrate 200 b opposed to the TFT substrate 200 a hasprotrusions 26 on the surface thereof facing the liquid crystal layer 30as an orientation-regulating structure. Each protrusion 26 has a shapeof a square truncated pyramid having slant sides 26 s and a top face 26t, and is roughly in the center of each square surrounded by thegrid-shaped openings 14 a.

In this embodiment, the openings 14 a of the picture-element electrode14, having a line width of 10 μm, surround a square having a size of 40μm×40 μm. The protrusion 26 has a bottom size of 20 μm×20 μm.

In the liquid crystal display device 200 having theorientation-regulating structures described above, when a voltage isapplied between the picture-element electrode 14 and the counterelectrode 24, liquid crystal molecules 30 a in a liquid crystal layer 30are oriented axially symmetrically with respect to the protrusion 26 asthe center as shown in FIGS. 9A and 9B. Although the change in theorientation direction of the liquid crystal molecules 30 a is shownsimply in FIG. 9A, the orientation direction of the liquid crystalmolecules 30 a actually changes sequentially with change of theazimuthal direction. A liquid crystal molecule 30 a existing at aposition in a certain azimuthal direction with respect to the protrusion26 is oriented in a direction substantially parallel to this azimuthaldirection.

As described above, the liquid crystal layer 30, which is in the stateof axially-symmetric orientation with respect to the protrusions 26 asthe center, has a plurality of (a myriad of) liquid crystal regions 31different in orientation direction, and thus the liquid crystalmolecules 30 a in each picture-element region are oriented in alldirections. In other words, each picture-element region of the liquidcrystal display device 200 is divided into an infinite number in termsof the orientation so that the liquid crystal molecules are oriented inall directions. In this embodiment, one liquid crystal domain, which isaxially symmetrically oriented with respect to the protrusion 26 as thecenter, is formed in correspondence with one square surrounded with thegrid-shaped openings 14 a when a voltage is applied. The “liquid crystaldomain” as used herein refers to a region in which the continuity oforientation of the liquid crystal molecules 30 a is maintained.

The TFT substrate 200 a of the liquid crystal display device 200 haslight-shield layers 40. As shown in FIG. 9B, each light-shield layer 40is formed to overlap (lie below) part of boundary region 33 defined asregion separating the plurality of liquid crystal regions 31 from oneanother. More specifically, the light-shield layer 40 is formed near thecenter of the liquid crystal domain, to oppose to the protrusion 26 ofthe counter substrate 200 b. In this embodiment, the light-shield layer40 is formed to be the same in shape as viewed in the direction normalto the substrate as the protrusion 26 and overlap the protrusion 26,that is, formed in a shape of a square having a side of 20 μm.

As shown in FIG. 9B, the region of the boundary region 33 that overlaps(lies above) the light-shield layer 40 is a region permitting the liquidcrystal molecules 30 a surrounding the region to tilt so that the endsof the liquid crystal molecules 30 a closer to the TFT substrate 100 a,that is, the substrate having the light-shield layer 40 go away fromthis region when a voltage is applied between the picture-elementelectrode 14 and the counter electrode 24.

The light-shield layer 40 formed as described above selectively shadesthe liquid crystal region 31 in which the liquid crystal molecules 30 afall toward the opposite to the observer, that is, the liquid crystalregion 31 of which the retardation value for light incident obliquelymonotonously increases with rise of the voltage, among the liquidcrystal regions 31 adjacent to each other via the boundary region 33.

In FIG. 9B, W6 denotes the width of a region shaded by the light-shieldlayer 40 during observation in the normal direction D6, and W7 denotesthe width of a region shaded by the light-shield layer 40 duringobservation in an oblique direction D7. As shown in FIG. 9B, duringobservation in the normal direction, the light-shield layer 40 shadesthe region of the liquid crystal layer 30 located right above thelight-shield layer 40. However, during observation in an obliquedirection, the light-shield layer 40 selectively shades the liquidcrystal region 31 in which the liquid crystal molecules 30 a fall towardthe opposite to the observer due to occurrence of parallax. FIG. 9B alsoshows the width W8 of a region shaded by the light-shield layer 40during observation in an oblique direction D8 opposite to the obliquedirection D7. As is found from FIG. 9B, during observation in theoblique direction D8, also, the light-shield layer 40 selectively shadesthe liquid crystal region 31 in which the liquid crystal molecules 30 afall toward the opposite to the observer.

As described above, the light-shield layer 40 selectively shades theliquid crystal region 31 in which the liquid crystal molecules 30 a tilttoward the opposite to the observer in whichever oblique direction theobserver observes the display device. Therefore, part of the liquidcrystal region 31 in which the liquid crystal molecules 30 a fall towardthe opposite to the observer fails to contribute to the display duringobservation in an oblique direction. This suppresses the increase of thetransmittance in the oblique direction during application of agray-scale voltage, and thus brings the voltage-transmittancecharacteristic obtained during observation in the oblique directionclose to the voltage-transmittance characteristic obtained duringobservation in the normal direction. As a result, the oblique-directiondisplay characteristics and the normal-direction display characteristicscan be made close to each other, and hence display free fromunnaturalness can be realized.

In this embodiment, the light-shield layer 40 was placed to overlap (liebelow) the region among the boundary regions 33 that corresponds to thecenter of the liquid crystal domain. Alternatively, the light-shieldlayer 40 may be placed to oppose to the region corresponding to aboundary between the adjacent liquid crystal domains. FIGS. 10A and 10Bshow a liquid crystal display device 200A having light-shield layers 40′overlapping (lying above) the boundaries between the adjacent liquidcrystal domains.

A counter substrate 200 b of the liquid crystal display device 200A hasthe light-shield layers 40′ formed to overlap (lie above) regions amongthe boundary regions 33 that correspond to the boundaries between theadjacent liquid crystal domains. That is, each light-shield layer 40′ isformed to overlap (lie above) the opening 14 a of the picture-elementelectrode 14. In other words, the region among the boundary regions 33that overlaps (lies below) the light-shield layer 40′ is a regionpermitting the liquid crystal molecules 30 a surrounding the region totilt so that the ends of the liquid crystal molecules 30 a closer to thecounter substrate 200 b, that is, the substrate having the light-shieldlayer 40′ go away from this region when a voltage is applied between thepicture-element electrode 14 and the counter electrode 24.

The light-shield layer 40′ of the counter substrate 200 b selectivelyshades the liquid crystal region 31 in which the liquid crystalmolecules 30 a fall toward the opposite to the observer, that is, theliquid crystal region 31 of which the retardation value for lightincident obliquely monotonously increases with rise of the voltage,among the liquid crystal regions 31 adjacent to each other via theboundary region 33, as in the case of the light-shield layer 40′ of thecounter substrate 10 b of the liquid crystal display device 100A shownin FIGS. 7A and 7B. In this way, in the liquid crystal display device200A, also, display free from unnaturalness can be realized.

The light-shield layers may be provided to correspond to both the centerof the liquid crystal domain and the boundaries between the liquidcrystal domains. FIGS. 11A and 11B shows a liquid crystal display device200B having the light-shield layers 40 and 40′ provided for both thecenter of the liquid crystal domain and the boundaries between theliquid crystal domains.

In the liquid crystal display device 200B, the TFT substrate 200 a hasthe light-shield layer 40 formed at the same position as that of thelight-shield layer 40 of the TFT substrate 200 a of the liquid crystaldisplay device 200, and the counter substrate 200 b has the light-shieldlayer 40′ formed at the same position as that of the light-shield layer40′ of the counter substrate 200 b of the liquid crystal display device200A.

In the liquid crystal display device 200B, also, in which thelight-shield layers 40 and 40′ selectively shade the liquid crystalregion 31 in which the liquid crystal molecules 30 a fall toward theopposite to the observer, display free from unnaturalness is realized.

Embodiment 3

The structure of a liquid crystal display device 300 of Embodiment 3according to the present invention will be described with reference toFIGS. 12A and 12B. FIG. 12A is a top view of the liquid crystal displaydevice 300 as viewed in the direction normal to the substrate, and FIG.12B is a cross-sectional view taken along line 12B-12B′ in FIG. 12A.FIGS. 12A and 12B show the state under application of a voltage acrossthe liquid crystal layer.

The liquid crystal display device 300 of Embodiment 3 is the same inconstruction as the liquid crystal display device 100 of Embodiment 1except for the position of the light-shield layers.

A counter substrate 300 b of the liquid crystal display device 300 has alight-shield layer 41 in each of a plurality of picture-element regions.The light-shield layer 41 is formed to overlap (lie above) a specificregion of the liquid crystal layer 30 as will be described later.

In the liquid crystal display device 300 in which each picture-elementregion is divided into four in terms of the orientation, the liquidcrystal molecules 30 a in each liquid crystal region 31 tilt at an angleof about 45° with respect to the polarization axes PA1 and PA2 of thepolarizing plates as shown in FIG. 12A. However, as shown in FIG. 13, ina region (oval-encircled region) 35, among the regions separating theadjacent liquid crystal regions 31 from each other, which is locatedbetween a bend 14 a′ of the opening 14 a and a bend 26′ of theprotrusion 26, the liquid crystal molecules 30 a tilt in a directionsubstantially parallel to the polarization axis PA1 of the polarizingplate in an attempt of maintaining the continuity of the orientation.

In the liquid crystal display device 300, the light-shield layer 41 isformed to overlap (lie above) the region 35 in which the liquid crystalmolecules 30 a tilt in a direction substantially parallel to thepolarization axis PA1 of the polarizing plate. In this embodiment, thelight-shield layer 41 is formed right on the counter electrode 24. Thecounter electrode 24 of the counter substrate 300 b has a thickness of100 nm (1000 Å), for example, and the light-shield layer 41 is placedsubstantially right on the liquid crystal layer 30 via the counterelectrode 24.

In Embodiments 1 and 2, described was the liquid crystal display devicecapable of suppressing unnaturalness that would otherwise be felt by theobserver due to the liquid crystal molecules tilting toward the oppositeto the observer. The liquid crystal display device 300 of Embodiment 3can suppress unnaturalness that may otherwise be felt by the observerdue to the liquid crystal molecules tilting in a direction substantiallyparallel to a polarization axis. This will be described in detail asfollows.

The conventional liquid crystal display device 1000 having nolight-shield layer shown in FIGS. 2A and 2B makes the observer feelunnatural due to the liquid crystal molecules 30 a tilting in adirection substantially parallel to a polarization axis for thefollowing reason.

When the liquid crystal display device 1000 is observed in an obliquedirection along the polarization axis PA2, liquid crystal molecules 30 atilting along the polarization axis PA2 (assuming that such liquidcrystal molecules 30 a exist although actually they hardly exist in theliquid crystal display device 1000) hardly cause a phase difference forlight incident obliquely to the liquid crystal layer 30, and thus do notaffect the display characteristics. However, liquid crystal molecules 30a tilting along the polarization axis PA1 (corresponding to the liquidcrystal molecules 30 a in the regions 35 shown in FIG. 13), which tiltto block the observation direction, cause a phase difference for lightincident obliquely to the liquid crystal layer 30. Moreover, suchregions in which liquid crystal molecules 30 a tilt in this directionexhibit a voltage-transmittance characteristic having the peaktransmittance at a gray-scale voltage.

FIG. 14 shows a voltage-transmittance curve L6 of the region in whichthe liquid crystal molecules 30 a tilt along the polarization axis PA1obtained when the liquid crystal display device 1000 is observed in anoblique direction along the polarization axis PA2. For comparison, FIG.14 also shows the voltage-transmittance curves L3 and L4 (shown in FIG.4) of the region in which the liquid crystal molecules 30 a tilt towardthe observer at an angle of 45° with respect to the polarization axesPA1 and PA2 and the region in which the liquid crystal molecules 30 atilt in the direction opposite to the observer at an angle of 45° withrespect to the polarization axes PA1 and PA2, respectively.

As is found from FIG. 14, in the region in which the liquid crystalmolecules 30 a tilt along the polarization axis PA1, the transmittancereaches the peak at a gray-scale voltage, causing inversion of thegradation of brightness. Therefore, if the proportion of existence ofsuch liquid crystal molecules 30 a in the picture-element region ishigh, breaking or inversion of the gradation becomes evident in thevoltage-transmittance characteristic obtained during observation in anoblique direction. This increases the difference between thenormal-direction display characteristics and the oblique-directiondisplay characteristics, and the resultant display makes the observerfeel unnatural.

In the liquid crystal display device 300 of this embodiment, thelight-shield layer 41 is placed to overlap (lie above) the region 35 inwhich the liquid crystal molecules 30 a tilt in a directionsubstantially parallel to the polarization axis PA1, to prevent thisregion 35 from contributing to the display. This suppresses excessiveincrease of the transmittance at a gray-scale voltage, and thus canbring the oblique-direction voltage-transmittance characteristic closeto the normal-direction voltage-transmittance characteristic. As aresult, since the oblique-direction display characteristics and thenormal-direction display characteristics can be brought close to eachother, display free from unnaturalness can be realized.

FIG. 15 shows a voltage-transmittance curve L7 obtained when the liquidcrystal display device 300 of this embodiment is observed in the normaldirection and a voltage-transmittance curve L8 obtained when it isobserved in an oblique direction (direction at a visual angle fallingalong the polarization axis PA2). For comparison, FIG. 15 also shows avoltage-transmittance curve L9 obtained when the conventional liquidcrystal display device 1000 is observed in the oblique direction. Notethat the voltage-transmittance curves shown in FIG. 15 are thoseobtained when the regions 35 in which the liquid crystal molecules 30 atilt roughly in parallel with the polarization axis PA1 occupy about 25%of each picture-element region.

As shown in FIG. 15, the voltage-transmittance curve L8 obtained whenthe liquid crystal display device 300 is observed in an obliquedirection is closer in shape to the voltage-transmittance curve L7obtained when it is observed in the normal direction than thevoltage-transmittance curve L9 of the display device having nolight-shield layer is. Therefore, natural display in which thenormal-direction display characteristics and the oblique-directiondisplay characteristics are close to each other is obtained.

The region in which the liquid crystal molecules 30 a tilt in adirection substantially parallel to the polarization axis does notcontribute to the transmittance obtained during observation in thenormal direction. Therefore, there is little loss in transmittance inthe normal direction by providing the light-shield layer shading onlysuch a region. To effectively shade only such a region, the light-shieldlayer should preferably be formed at a position that can preventoccurrence of parallax. In view of this, the light-shield layer ispreferably formed substantially right on the liquid crystal layer sothat the spacing of the light-shield layer from the liquid crystal layeris as small as possible. The effect of improving the displaycharacteristics may be obtained when the light-shield layers are placedto cover only part of the regions in which the liquid crystal molecules30 a tilt in a direction substantially parallel to the polarizationaxis. However, from the standpoint of further improving the displayquality, the light-shield layers are preferably placed to cover alargest possible portion of such regions, more preferably placed tocover substantially all of such regions.

The effect of improving the display quality, obtained by placing thelight-shield layers to overlap (lie above or below) the regions in whichthe liquid crystal molecules tilt in a direction substantially parallelto the polarization axis, is significant in a liquid crystal displaydevice having such regions in a comparatively high proportion.

For example, in the liquid crystal display device 1000 shown in FIGS. 2Aand 2B, if the pitch of bends of each opening 14 a and protrusion 26(corresponding to P′ in FIG. 13) is small, the proportion of the regionsin which the liquid crystal molecules tilt in a direction substantiallyparallel to the polarization axis PA of the polarizing plate in eachpicture-element region is high. This will increase the differencebetween the normal-direction display characteristics and theoblique-direction display characteristics, and as a result, makeunnaturalness of the display evident.

In view of the above, in a liquid crystal display device having suchregions in a comparatively high proportion, a light-shield layer shadingthe regions in which the liquid crystal molecules 30 a tilt in adirection substantially parallel to the polarization axis, like thelight-shield layer 41 in the liquid crystal display device 300 of thisembodiment, may be placed in addition to a light-shield layerselectively shading the liquid crystal regions in which the liquidcrystal molecules tilt toward the opposite to the observer (thelight-shield layers 40 and 40′ in the liquid crystal display devices 100and 200 of Embodiments 1 and 2). By this placement, the display qualitycan be further improved.

Light-shield layers shading the regions in which the liquid crystalmolecules 30 a tilt in a direction substantially parallel to thepolarization axis (light-shield layers roughly the same as thelight-shield layers 41 in the liquid crystal display device 300 ofEmbodiment 3) were additionally placed in the liquid crystal displaydevice 100 of Embodiment 1, and the effect of improving the displayquality by this additional placement was examined.

FIG. 16 shows a voltage-transmittance curve L10 obtained when the liquidcrystal display device 100 is observed in the normal direction, avoltage-transmittance curve L11 obtained when it is observed in anoblique direction (direction at a visual angle falling along thepolarization axis PA2), and a voltage-transmittance curve L12 obtainedwhen a liquid crystal display device having the additional light-shieldlayers described above is observed in an oblique direction. Thevoltage-transmittance curves shown in FIG. 16 are those obtained whenthe proportion of the regions in which the liquid crystal molecules 30 atilt in a direction substantially parallel to the polarization axis PA1is about 25%.

As shown in FIG. 16, the voltage-transmittance curve L12 obtained byplacing the additional light-shield layers is closer in shape to thenormal-direction voltage-transmittance curve L10 than thevoltage-transmittance curve L11 obtained without the additionallight-shield layer is. Therefore, by placing the additional light-shieldlayers, the oblique-direction display characteristics become closer tothe normal-direction display characteristics, and thus the displayquality can further be improved.

Embodiment 4

FIG. 17 shows a liquid crystal display device 400 of Embodiment 4according to the present invention. The liquid crystal display device400 shown in FIG. 17 has the same construction as the liquid crystaldisplay device 200 of Embodiment 2 except for the position of thelight-shield layers.

The counter substrate (not shown) of the liquid crystal display device400 has a light-shield layer 41 in each of the plurality ofpicture-element regions. The light-shield layer 41 is formed to overlap(lie above) regions in which the liquid crystal molecules 30 a tilt indirections substantially parallel to the polarization axes PA1 and PA2of the polarizing plates. In the example shown in FIG. 17, thepolarization axes PA1 and PA2 of the polarizing plates are arranged inparallel with the two directions in which the openings 14 a of thepicture-element electrodes 14 extend, and the light-shield layer 41 hasa shape of a cross composed of two sides extending parallel to thepolarization axes PA1 and PA2.

In the liquid crystal display device 400, the light-shield layer 41 isplaced to overlap (lie above) regions in which the liquid crystalmolecules 30 a tilt in directions substantially parallel to thepolarization axes PA1 and PA2 of the polarizing plates. Therefore, as inthe liquid crystal display device 300 of Embodiment 3, natural displayfree from unnaturalness can be realized.

In the liquid crystal display device 300 of Embodiment 3, thelight-shield layer 41 was placed to overlap (lie above) only the regionsin which the liquid crystal molecules 30 a tilt in a directionsubstantially parallel to the polarization axis PA1 considering the factthat there hardly exist liquid crystal molecules 30 a tilting in adirection substantially parallel to the polarization axis PA2. In theliquid crystal display device 400 of this embodiment, there exist liquidcrystal molecules 30 a tilting along the polarization axis PA2 as wellas those tilting along the polarization axis PA1. Therefore, thelight-shield layer 41 is placed to cover the regions including suchliquid crystal molecules 30 a.

The light-shield layer 41 may be placed to overlap (lie above) onlyeither the regions in which the liquid crystal molecules 30 a tilt alongthe polarization axis PA1 or the regions in which the liquid crystalmolecules 30 a tilt along the polarization axis PA2. However, morenatural display can be realized by placing the light-shield layer 41 tocover both regions.

If the polarization axes of the polarizing plates are arrangeddifferently for liquid crystal cells having roughly the sameconstruction, the regions in which liquid crystal molecules tilt indirections substantially parallel to the polarization axes are differentbetween these liquid crystal cells. Therefore, for differentarrangements of the polarization axes, it should be ensured that thelight-shield layer is placed so as to cover regions including suchliquid crystal molecules. FIG. 18 shows a liquid crystal display device400A in which the arrangement of the polarization axes PA1 and PA2 ofthe polarizing plates is different from that in the liquid crystaldisplay device 400.

In the liquid crystal display device 400A shown in FIG. 18, thepolarization axes PA1 and PA2 are arranged to form an angle of 45° withthe two directions of extension of the openings 14 a of thepicture-element electrodes 14. Therefore, the light-shield layer 41 ofthe liquid crystal display device 400A has a shape obtained by rotatingthe light-shield layer 41 of the liquid crystal display device 400 by45° in the plane parallel to the substrate plane.

In the liquid crystal display device 400A, also, the light-shield layer41 is placed to cover regions in which the liquid crystal molecules 30 atilt in directions substantially parallel to the polarization axes PA1and PA2 of the polarizing plates. Therefore, as in the liquid crystaldisplay device 400, natural display free from unnaturalness can berealized.

Thus, according to the present invention, a liquid crystal displaydevice with high display quality that has a wide viewing anglecharacteristic and can provide display free from unnaturalness isprovided.

While the present invention has been described in preferred embodiments,it will be apparent to those skilled in the art that the disclosedinvention may be modified in numerous ways and may assume manyembodiments other than that specifically set out and described above.Accordingly, it is intended by the appended claims to cover allmodifications of the invention that fall within the true spirit andscope of the invention.

1-19. (canceled)
 20. A liquid crystal display device comprising: a firstsubstrate, a second substrate, and a substantially vertical alignmenttype liquid crystal layer including liquid crystal molecules havingnegative dielectric anisotropy disposed between the first substrate andthe second substrate; the device having a plurality of picture-elementregions each defined by a first electrode placed on the first substrateon the side facing the liquid crystal layer and a second electrodeplaced on the second substrate to oppose to the first electrode via theliquid crystal layer; in each of the plurality of picture-elementregions, the liquid crystal layer having a plurality of liquid crystalregions different in the direction in which liquid crystal moleculestilt when a voltage is applied between the first electrode and thesecond electrode; wherein at least one of the first substrate and thesecond substrate comprises a light-shield layer overlapping at leastpart of boundary region defined as regions separating the plurality ofliquid crystal regions from each other; the at least part of boundaryregion overlapping the light-shield layer is a region permitting liquidcrystal molecules surrounding the region to tilt so that ends of theliquid crystal molecules closer to the substrate having the light-shieldlayer go away from the region when a voltage is applied between thefirst electrode and the second electrode, and the light-shield layer isplaced with a spacing of 3 μm or more from the liquid crystal layer. 21.The liquid crystal display device of claim 20, wherein the spacingbetween the light-shield layer and the liquid crystal layer is 5 μm ormore.
 22. The liquid crystal display device of claim 20, furthercomprising: a pair of polarizing plates placed opposing to each othervia the liquid crystal layer so that their polarization axes aresubstantially perpendicular to each other; wherein in each of theplurality of picture-element regions, at least one of the firstsubstrate and the second substrate has an additional light-shield layeroverlapping at least part of regions in which liquid crystal moleculestilt in directions substantially parallel to the polarization axes ofthe pair of polarizing plates when a voltage is applied between thefirst electrode and the second electrode.
 23. The liquid crystal displaydevice of claim 20, wherein at least one of the first substrate and thesecond substrate has at least one protrusion having a slant side formedon the surface facing the liquid crystal layer, and the direction inwhich liquid crystal molecules tilt in each of the plurality of liquidcrystal regions is defined by orientation-regulating force of the atleast one protrusion.
 24. The liquid crystal display of claim 20,wherein at least one of the first electrode and the second electrode hasat least one opening, and the direction in which liquid crystalmolecules tilt in each of the plurality of liquid crystal regions isdefined by an inclined electric field generated at an edge portion ofthe at least one opening when a voltage is applied between the firstelectrode and the second electrode.
 25. The liquid crystal displaydevice of claim 20, wherein at least one of the first substrate and thesecond substrate has at least one protrusion having a slant side formedon the surface facing the liquid crystal layer; at least one of thefirst electrode and the second electrode has at least one opening; andthe direction in which liquid crystal molecules tilt in each of theplurality of liquid crystal regions is defined by orientation-regulatingforce of the at least one protrusion and an inclined electric fieldgenerated at an edge portion of the at least one opening when a voltageis applied between the first electrode and the second electrode.
 26. Theliquid crystal display device of claim 20, wherein the first substratefurther includes switching elements respectively placed to correspond tothe plurality of picture-element regions, and the first electrodecomprises a plurality of picture-element electrodes respectively placedfor the plurality of picture-element regions and switched with theswitching elements, and the second electrode comprises at least onecounter electrode opposed to the plurality of picture-elementelectrodes.